1. Field of the Invention
The invention relates to a semiconductor component, comprising a semiconductor substrate which exhibits on a main surface a contact area for a main electrode and a contact area for a control electrode, a main electrode and a contact electrode which are in contact with the semiconductor substrate, the main electrode exhibiting a groove in which the control electrode and a spring, which presses the control electrode against the semiconductor substrate, are accommodated, and a control electrode access line.
2. Discussion of Background
A number of controllable semiconductor components for relatively high power are characterized by the fact that high currents occur for a short time at the control electrode. These elements include, for example, the gate-turn-off (GTO) thyristor in which the high currents are required for turning off the element. It is of importance for the proper operation of such semiconductor components that the entire gate area of the semiconductor substrate is supplied without delay and uniformly with current. It has been found in the past that this can be achieved most easily by means of an annnularly constructed control electrode.
It is then a matter of finding an arrangement in which the contact areas for main and control electrode, located on the same main surface of the semiconductor substrate, can be accurately connected to main and control electrode.
Such a possible arrangement is disclosed in DE-A1 35 38 815. The corresponding component is described as follows:
A round semiconductor substrate has on a main surface a contact area for a main electrode and one such for a control electrode. The contact area for the control electrode is annular so that that for the main electrode is divided into two separate regions (a circle and an enclosing ring). The main electrode is a round plate which exhibits on the side facing the semiconductor substrate an annular groove wherein the annular control electrode is accommodated. The control electrode is displacable in the vertical direction in the groove and is held in contact with the semiconductor substrate by a spiral spring also accommodated in the groove.
A plastic film of fluorinated plastic applied to the control electrode is used as insulation between control and main electrode. The side of the control electrode facing the semiconductor substrate is left open in the plastic film and coated with silver for the purpose of improving the ohmic contact.
The control electrode is accessed via a line wire. Between the main electrode and the semiconductor substrate, a reinforcing plate of molybdenum is located which is also used for reducing thermal stresses in the semiconductor substrate.
The control electrode is produced as follows. A metal ring (for example of copper) having the required dimensions and tolerance is taken, the surface is masked in such a manner that the contact area to the semiconductor substrate and the connecting point for the line wire can be formed and the required plastic is sprayed on which forms the insulation film with respect to the main electrode. The line wire is soldered to the place provided for this purpose on the control electrode. The surface free of plastic facing the semiconductor substrate is coated with silver and tempered.
The problem of the semiconductor component just described, disclosed in DE-A1 35 38 815, lies in its inadequate mechanical ruggedness and in its expensive production method. This particularly applies to the control electrode. The coating with plastic is found to be risky in practice. On the one hand, the choice of plastic is restricted by the fact that it should adhere well to the metal surface of the control electrode and, on the other hand, a uniform crack-free film formation cannot be easily achieved. Furthermore, the masking technique is always associated with considerable expenditure.